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fs/drop_caches.c: avoid softlockups in drop_pagecache_sb()

When superblock has lots of inodes without any pagecache (like is the case for /proc), drop_pagecache_sb() will iterate through all of them without dropping sb->s_inode_list_lock which can lead to softlockups (one of our customers hit this). Fix the problem by going to the slow path and doing cond_resched() in case the process needs rescheduling.

Jan Kara committed 7 years ago

Commit c27d82f1 parent e0a352f1 file · +7 −1Browse files

Unified · Split

fs/drop_caches.c+7−1
@@ -21,8 +21,13 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused) · 20 unmodified lines
21 spin_lock(&sb->s_inode_list_lock);21 spin_lock(&sb->s_inode_list_lock);
22 list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {22 list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
23 spin_lock(&inode->i_lock);23 spin_lock(&inode->i_lock);
24 /*
25 * We must skip inodes in unusual state. We may also skip
26 * inodes without pages but we deliberately won't in case
27 * we need to reschedule to avoid softlockups.
28 */
24 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||29 if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
25 (inode->i_mapping->nrpages == 0)) {30 (inode->i_mapping->nrpages == 0 && !need_resched())) {
26 spin_unlock(&inode->i_lock);31 spin_unlock(&inode->i_lock);
27 continue;32 continue;
28 }33 }
@@ -30,6 +35,7 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused) · 1 unmodified line
30 spin_unlock(&inode->i_lock);35 spin_unlock(&inode->i_lock);
31 spin_unlock(&sb->s_inode_list_lock);36 spin_unlock(&sb->s_inode_list_lock);
32 37
38 cond_resched();
33 invalidate_mapping_pages(inode->i_mapping, 0, -1);39 invalidate_mapping_pages(inode->i_mapping, 0, -1);
34 iput(toput_inode);40 iput(toput_inode);
35 toput_inode = inode;41 toput_inode = inode;